1. Technical Field
This invention relates to a method and apparatus for processing video data, and in particular to processing video data captured on a mobile video data capture means.
2. Description of Related Art
Video conferencing is a discussion between two or more people who are in different places but can see and hear each other using electronic communications. One goal in offering video conferencing is to enhance the conference by transmitting more of the non-verbal aspects of the conversation. Making the assumption that a major contributing factor to these aspects is the appearance of expressions on the face of a conference participant, it is desirable to present these expressions as clearly and consistently as possible.
In mobile video conferencing, at least one of the video conferencing participants uses a camera equipped mobile communications device and is therefore able to move whilst remaining within the field of view of the camera.
The appearance of a video conferencing participant in a frame of video captured by a camera equipped mobile communications device is subject to variations in position, size, orientation, lighting direction and colour.
Position, size and orientation changes are due to the relative global motion between the participant and the camera. Conventional techniques for detecting moving objects such as background subtraction and frame differencing will not work as they assume that the background is stationary, which is not the case if the user himself is moving.
As the conference participant moves through an environment with many light sources or causes rotation of the mobile communications device, there will be substantial changes in the direction from which the light falls on the participant's face and also substantial changes in colour of the face due to the changes of the incident light falling on the face or the result of light reflected from coloured objects. These lead to gradual but substantial changes in the intensity and colour of the pixels that make up the image of the face. If the raw video data is subsequently encoded in order to meet a low ‘maximum bit rate’ requirement, there will be a trade off between coding these variations and the clarity of facial expressions and as a result the variations will diminish the clarity of the facial expressions.
Additionally, in current camera equipped mobile communications devices white balance compensation is sometimes applied to the image. White balance compensation seeks to adjust the gains of the red, green and blue (RGB) channels of the image so that the total brightness of the channels are equal. This can result in the face (which only forms a portion of the image) appearing green or blue.